Sequential analysis of apoptosis induction in peripheral blood mononuclearcells and lymph nodes in the early phase of pathogenic and nonpathogenic SIVmac infection

To investigate the role of apoptosis in the early phase of HIV infection, w e used macaques infected with sinian immunodeficiency virus strain mac (SIV mac) as a primate model and examined sequentially the characteristics of ap optosis of lymphocytes in peripheral blood mononuclear cells (PBMCs) and ly mph nodes in the early phase of SIVmac infection. Five macaques infected wi th a pathogenic strain of SIV, SIVmac239, were analyzed during the first 4 weeks after infection, Peripheral CD4(+) and CD8(+) cells transiently decre ased at 1 week postinfection, The percentage of apoptotic cells in cultured PBMCs increased from about 2 weeks postinfection, The number of apoptotic cells in lymph node sections was higher on days 13 and 28 postinfection tha n before infection and on day 5 postinfection, Fas antigen expression on pe ripheral lymphocytes was upregulated from day 8 postinfection, These result s indicate that apoptosis is induced about 2 weeks after SIVmac239 infectio n, following the upregulation of Fas antigen expression on lymphocytes, Sin ce apoptosis was induced about 1 week after the decrease in peripheral CD4( +) and CD8(+) cell counts, it appears that the apoptosis induction does not play an important role in the transient lymphopenia in the early phase of SIVmac infection, In macaques infected with a nonpathogenic derivative of S IVmac239, SIVmac Delta nef, apoptosis of lymphocytes was induced as it was in SIVmac239-infected macaques, but to a lesser degree, suggesting a correl ation between the extent of apoptosis induction in lymphocytes in the early phase of SIVmac infection and the pathogenicity of SIVmac.